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Patch "x86/entry/compat: Keep TS_COMPAT set during signal delivery" has been added to the 4.5-stable tree

PATCH [email protected] 1 participant 1 message Apr 9, 2016

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This is a note to let you know that I've just added the patch titled

x86/entry/compat: Keep TS_COMPAT set during signal delivery

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-entry-compat-keep-ts_compat-set-during-signal-delivery.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 4e79e182b419172e35936a47f098509092d69817 Mon Sep 17 00:00:00 2001

From: Andy Lutomirski <[email protected]>
Date: Wed, 10 Feb 2016 14:15:27 -0800
Subject: x86/entry/compat: Keep TS_COMPAT set during signal delivery

From: Andy Lutomirski <[email protected]>

commit 4e79e182b419172e35936a47f098509092d69817 upstream.

Signal delivery needs to know the sign of an interrupted syscall's return value in order to detect -ERESTART variants. Normally this works independently of bitness because syscalls internally return long. Under ptrace, however, this can break, and syscall_get_error is supposed to sign-extend regs->ax if needed.

We were clearing TS_COMPAT too early, though, and this prevented sign extension, which subtly broke syscall restart under ptrace.

Reported-by Robert O'Callahan <[email protected]>
Signed-off-by Andy Lutomirski <[email protected]>
Cc Al Viro <[email protected]>
Cc Andy Lutomirski <[email protected]>
Cc Borislav Petkov <[email protected]>
Cc Brian Gerst <[email protected]>
Cc Denys Vlasenko <[email protected]>
Cc H. Peter Anvin <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Shuah Khan <[email protected]>
Cc Thomas Gleixner <[email protected]>
Fixes c5c46f59e4e7 ("x86/entry: Add new, comprehensible entry and exit handlers written in C")
Link http://lkml.kernel.org/r/cbce3cf545522f64eb37f5478cb59746230db3b5.1455142412.git.luto@kernel.org open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/entry/common.c |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)
arch/x86/entry/common.c +13 -10
@@ -268,6 +268,7 @@ static void exit_to_usermode_loop(struct
 /* Called with IRQs disabled. */
 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 {
+	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	u32 cached_flags;
 
 	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))

@@ -275,12 +276,22 @@ __visible inline void prepare_exit_to_us
 
 	lockdep_sys_exit();
 
-	cached_flags =
-		READ_ONCE(pt_regs_to_thread_info(regs)->flags);
+	cached_flags = READ_ONCE(ti->flags);
 
 	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 		exit_to_usermode_loop(regs, cached_flags);
 
+#ifdef CONFIG_COMPAT
+	/*
+	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
+	 * returning to user mode.  We need to clear it *after* signal
+	 * handling, because syscall restart has a fixup for compat
+	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
+	 * selftest.
+	 */
+	ti->status &= ~TS_COMPAT;
+#endif
+
 	user_enter();
 }
 

@@ -332,14 +343,6 @@ __visible inline void syscall_return_slo
 	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 		syscall_slow_exit_work(regs, cached_flags);
 
-#ifdef CONFIG_COMPAT
-	/*
-	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
-	 * returning to user mode.
-	 */
-	ti->status &= ~TS_COMPAT;
-#endif
-
 	local_irq_disable();
 	prepare_exit_to_usermode(regs);
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/x86-entry-compat-keep-ts_compat-set-during-signal-delivery.patch